Broadcast antenna



June27, 1950 w. DARL-ING 2,513,007

BROADCAST ANTENNA Filed May 11, 1945 2 Sheets-Sheet 1 Z 2 l l 1 2 l INVENTOR.

ATTORNEY June 27, 1950 w. DARLING BROADCAST ANTENNA Filed May 11, 1945 2 Sheets-Sheet 2 INVENTOR Woooeow DARL l/vq BY /WW ATTORN EY Patented June 27, 1950 BROADCAST ANTENNA Woodrow Darling, Merchantville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application May 11, 1945, Serial No. 593,152

Claims.

The present invention relates to broadcast antennas and, more particularly, to such antennas designed for ultra short wave operation.

An object of the present invention is the provision of a high frequency broadcast antenna requiring a minimum number of feed points from the transmission line to the antenna structure itself.

A further object of the present invention is the provision of a high frequency antenna which does not require a number of bazookas or high impedance trap circuits along the transmission line to prevent the flow of high frequency energy along the outside of the transmission line.

A'further object of the present invention is the provision of a high frequency broadcast antenna having substantially a uniform horizontal radiation pattern.

Still a further object of the present invention is the provision of a high frequency broadcast antenna radiating horizontally polarized energy.

Still another object of the present invention is the provision of a multilayer high frequency broadcast antenna having a high gain per layer.

Still a further object of the present invention is the provision of a wide band high frequency broadcast antenna.

Still another object of the present invention is the'provision of a high frequency broadcast antenna which is characterized by simplicity of mechanical construction and which is furthermore electrically grounded for protection from lightning strokes.

An additional object of the present invention is to provide an antenna having a minimum numher of feed points and uniform horizontal pat- V tern" of horizontally polarized radiation and whcrein'a circular current flow in horizontal planes in the antenna is obtained.

The foregoing objects and others whichmay appear from the following detailed description are attained by providing an antenna in the form of a vertically disposed hollow conductive cylinder having a circumference equal to a half wavelength at the operating frequency and an overall length, in a preferred elemental embodiment, equal to onewavelen'gth. A narrow longitudinal slot closed at each end is provided along the length of the cylinder. It has been found that by appropriately adjusting the width of the longitudinal slot and the length of the slot, a band width of up to 12 or. 15 percent of the midband frequency may-be satisfactorily obtained.

Also in a preferred form of the invention a transmission line-for connecting the antenna to turned inwardly to form flanges the associated transmitting and/or receiving equipment is coupled across the slot at a position midway between its ends.

The structure as so far described may be stacked in a number of vertical layers in order to I increase the vertical directivity to any desired extent.

The present invention will be more fully understood by reference to the following detailed description which is accompanied by a drawing in which:

Figure 1 illustrates in elevation an embodiment of the present invention;

Figure 2 illustrates in horizontal cross section a view of the antenna of Figure 1 taken at line 2, 2 of Figure 1;

Figure 3 illustrates in vertical section a modification of the present invention utilizing a pair of vertically stacked antennas such as those shown in Figure 1 to increase the vertical directivity;

Figure 4 illustrates in vertical section a further modification of the present invention utilizing a vertically stacked array of three antennas "similar to that shown in Figure 1.

Figure 5 illustrates in vertical section a modified form of the invention shown in Figure 3 wherein a different manner of connecting th feed line is utilized.

1);. Referring now toFigures l and 2, there is shown a broadcast antenna in the form of a ver----. tically disposed hollow conductive cylinder 10,,"- having a longitudinal slot l2 extending from one The edges of slot I2 may be '1 l3 and My end to the other.

though outwardly extending flanges may be used if desired.

problem of making connections from the trans- .mission line to the antenna itself. The slot [2 is preferably electrically closed at each end. A

simple way of closing the slot I2 is shown in Figures 1 and 2 wherein short pieces of pipe l6, [6, one at each end of the slot, rest between flanges l3, l4. 'Bolts ll pass through holes in flanges l3, l4 and through pipe section l6, l6 rigidly clamping the flanges l3 and I4 against the ends of pipe sections l6, IS.

The antenna is connected to a'transr'nitter or receiver by means of transmission line TL having an outer sheath l8 and inner conductor 20 The These flanges provide additional structural rigidity and somewhat simplify the;

Here the outer stantially purezcircumtenential excitation of the antenna, and a total absence of longitudinal excitation.

The outer shell I8 is preferably bonded to the interior of the hollow cylinder in at several pointswtwo equal length branches T141 and TL2. Transmission line TL]. crosses and is connected to the upper slot 22 at substantially its midpoint. while transmission line TLz also crosses and is directly connected to the lower slot 32 at substantially its midpoint. The other ends of transmission lines TL; and 11-2 are connected togethe'rflinia parallel relationship: and: then connected to transmision lindTL. when the transmission lines are thus connected, it is of course desirable that the transmission line TL have a characteristic impedance one-half that of the characteristic impedance of each of transmission along its length so that no difference in potential V v may exist at any point between the sheath linesiTlii or=TLz"in-"order that standing waves and interior of the hollow 'cylirid'en'll)at"*the"15"shall'not-beSetupLin transmission line TL. The line along which shell l8 lies. Generally this vertical stacking oftwo radiators serves subis immediately adjacent fiangesxhwllfndesiredg stantially' tow'comprfess the radiation in a narrow flanges l3, [4 may be turned outwardly, in .which. angle, thereby increasing the effectiveness of the case it may be preferred. to run transmiss'ion line TL along flange M on the exterior surface of tube-ma As indicated in- Figure the hollow conductive cylinder ll) has an exterior-'-circumterence "sub 7 stahtially" equal-to 'one'half of'a wavelength at thefoperatin'g frequency: length ofthe an tennafithat is, its" dimension measured alongthe slot, is preferably equal to one wavelength at theop'erating -frequency as illustrated-inl i'gure 1;

However this "dimension is -not 1 critical and-*may be *c'on'sidefably decreasedin -increased. In :the multielement arrays, to be described later, where In an embodiment of the antennev-shown' -in Figures l and 2, actuallybonstructed and opera ated- 'over 11a frequency 1 range? =o-f :rrcm 90 to- 104"- Y megacycle's'; the-hollowconductive cylinder- In had ii-the?rslotsiinzancin rphase relationship-.151.

Aside nfrom: athea i increasedr.zvertica;l directivity; thatais the? compress-ion of the i radiate'cr energyz intora narrowyertical: anglexthe operationof the antenna ofrrFigure'4 is' thesanie-lasithe nperar-m 45 etio-n cof --;previously =7described-embodiments ;s; that:

is, currentsfflow circumferentially .over'the' ex teriors'urface of the system givenarisetto'liradisza a diameter of m inches and an: overall length of 12 feet.- Slot l2 was 3 inches wide while flanges" I I3, -'l 4 hada width- 01" about an inch and:: a halt? l This resulted in a: driving point-impedance connected to a 50 ohinrcoaXial -line -without in-" troducingza serious mismatch 'zbetween lineiiandi a The driving point impedahc'e' may be antenn varied to some: extent 'by warying'tthefawi'dth' of slot l2 A horizirintal field pattern: taken indicated that:

over aboveementionedrfrequency rangedzhe're W383i. no morerthanfi 'db variation in i field strengthlin 1 the zhorizontal plane:rsurrounding'lftlrieantenna, thuss establishing:thezefact that theantennais .1

well suite'd for broadcastingcusen A ssimilar: iantermamwas ralsoarconstructed land therhorizontaleplanex Figurecll illustrates a; modifieddorm ofrthe in-v I ventionz r. Two antennas-reachconstructed imam;

cordance with-.Figures 1 andz2, are stacked'one'..-1 above tithe other; thusz makingiza tota'lizoverall height of two wavele'ngths's Theiloiigitudinalr slot: divided t-into" two r parts 22 and 32, eachnhavingza lehgthmubstahtially:

equal to?oner wavelengtnmby; intermediate metal spacing bar -|B" dire'ctly (electrically connecting-'1 together the? midpoin'ts zz'of '-"fia,-nges' 11 3;." l 4, I ordei to feed the slots in an in phase relationn75 necte'dsto the outer sheaths lw, 58 oftransmissionship the transmission lin'e-TL; Was' diVid'ed into:

antenna ina'll horizontal directions.

Figure 4 illustrates a further modification of the: present invention :wherein three antennas are'rstacked terticallyf'in"'layers one-above the other. The ho'llo'w cylindrical conductor "4- 0* thus hasa an overall len'gth 'of :thr'eewavelengths-. In rthis'rmodifi cation the cylinder "has athree =slots"=-'+ 42 5' 5 slam- 44: milled ior otherwise'Fcutin *an end to-enct relationship along ion'elsidei'of the' cylirid 4B. The slots do not quite meet nor do they come quite ztotlre fl'ends".'of cylindeititllia Thus cor1duc= 5- itivei bridgesifl 5;=:4 6; 141: and: 4 8 are -formed=; divitl 1 ingzwh'at would otherwisexbewne .continuousrslot intorthrfeerendatoaendslots reach-having a; length substantiallyiequal =.to'i onerwavelengthz s;

The mainiitransmissionFIineF'TL ini'this m'odifi 'c: i-cationris divide'dzinto'athreebranches. TLr,: IL2 and:

TLzlconnected' acrossrslots 42,313: and .:Mi -heretoforerdescribedxt The slengthsnl of transmission: lines TLi, TLz and TL: must all ber'equal isoi thatvntherenergytfromthertransmittercis applied across ation sofa-horizontally polarized". radiation fall:

directions toward the horizoniwvhen-ithe :antenna'? 7:. is mounted'with its axisvertical: and whentran'sr' mission-"line'TL is connected to a suitable trans-11 mitten Figure 5 illustrates a different way ofrifeedingn:

thenan tenna of: Figure 3. LI-Iereg'. th'ei \in'ner."con-" 5 ,ductor -50 -01? transmission line is connected to? thel-left-hand': edge of slot22 *andicross'e's-to the" rightehand I'side where it enters; the: outer: sheath: T 48 GfEtIaIISmiSS'iOIIJiIIE T111. Therinnericonductor of transmissionilinesTLz is conirrected to thev right-hand 'edge of slot 32 =andybrossingslot"32' at theileft-hand edge; enters the: outer 'sheaths58' of transmission line T1112. .Thus," .these'=two 'tra'ns-sr mission dines-must be fed: a phase opposing. re-r lationshipi The pha'senopposing relationship is obtained by connecting: linese-TLif and Tile to trans:

mission-line-TL throughna linebalancerconverter transmission.nline' TT An .:outer? sheath 1-1 I "sur rounds the:sendt'ofstheflsheath l8 of transmission line TL for a" dist'ance equal'to' one-quarterof t operating'wave-length and- -is conductively con-- While I have illustrated a particular embodiment of the present invention, it should be clearly understood that it is not limited thereto since many modifications may be made in the several elements employed and in their arrangement which will fall within the spirit and scope of the invention.

. What is claimed is:

..1.' A broadcast antenna including a hollow conductive cylinder having a length substantially equal to one wavelength at the operating frequency and having a circumference of the order of one-half wavelength, there being a narrow longitudinal slot along the length of said cylinder and a coaxial transmission line connected to the edges of said slot at a position half way between the ends of said slot and extending longi-' tudinally along said slot inside of said cylinder and out one end of said cylinder.

2. A broadcast antenna including a hollow conductive cylinder having a length substantially equal to one wavelength at the operating frequency and having a circumference of the order of one-half wavelength, there being a narrow longitudinal slot along the length of said cylinder and a coaxial transmission line extending longitudinally from a position half Way between the ends of said slot and along said slot inside of said cylinder and out one end of said cylinder, said coaxial line having an inner conductor extending across said slot and connected to the opposite edge of said slot and said line having an. outer sheath connected along the edge of said slot from one end of said antenna to substantially the midpoint of said slot.

3. A broadcast antenna including a hollow conductive cylinder having a circumference substantially equal to one-half wavelength at the operating frequency and a length equal to a multiple of wavelengths, said cylinder having a number of longitudinal slots spaced a multiple of wavelengths including unity apart along the length of said cylinder in an end to end relationship, each of said slots having a length equal to one wavelength and being closed at each end, a coaxial transmission line connected across the midpoint of each of said slots at the edges thereof and means for connecting each of said transmission lines in a parallel relationship to another transmission line which is adapted to connect said antenna to transducer equipment, said first mentioned transmission lines having the same length and each extending longitudinally along the edge of the slot with which it is associated to one end thereof.

4. A broadcast antenna including a hollow conductive cylinder having a circumference substantially equal to a half wavelength of the operating frequency, an overall length equal to two wavelengths, a pair of narrow longitudinal slots arranged in an end to end relationship along the length of said cylinder, each of said slots having a length lying between three-quarters and one wavelength and being electrically closed at each end, a coaxial transmission lin connected across the midpoint to each of said, slots at the edges thereof and further means for connecting each of said transmission lines in a parallel relationship to a further transmission line adapted to connect said antenna to transducer equipment, said first mentioned transmission lines having the same length and each extending along an edged the slot with which it is associated to one end thereof.

5. A broadcast antenna including a hollow conductive cylinder having a circumference substantially equal to a half wavelength of the operating frequency and a length equal to two wavelengths, a pair of narrow longitudinal slots extending along the length of said cylinder in an end to end relationship, each of said slots having a length substantially equal to one wavelength, said slots being closed at each end, coaxial transmission lines each having an outer sheath and an inner conductor connected across the midpoints of each of said slots at the edges thereof, the inner conductor of one of said lines crossing said slots in an opposite direction from the other and means within said cylinder for connecting said transmission lines in a series relationship to the end of another transmission line.

6. A broadcast antenna including a hollow conductive cylinder having a circumference substantially equal to one-half of the operating wavelength and having a narrow longitudinal slot along the length of said cylinder, inwardly turned flanges along each edge of said slot, conductive means joining said flanges together at points along said slot spaced substantially one wavelength apart and a coaxial transmission line having inner and sheath conductors connected to the edges of said slot at points intermediate said first mentioned points said coaxial transmission line extending along said slot inside said cylinder in conductive relationship thereto and out one end thereof.

7. A broadcast antenna including a conductive member constituted by a conductive surface element arranged in the form of a substantially closed hollow member having a narrow longitudinal slot along the length thereof, said member having a length substantially equal to one wavelength at the operating frequency and a mean circumferential dimension of the order of onehalf wavelength, and a coaxial transmission line connected to the edge of said slot at a position halfway between the ends of said slot and extending longitudinally along said slot inside of said member and out one end thereof.

8. A broadcast antenna including a hollow conductive member in the form of a substantially continuous surface of revolution, said member having a length substantially equal to one wavelength at the operating frequency and having a circumference of the order of one-half wavelength, there being a narrow longitudinal slot along the length of said member and a coaxial transmission line connected to the edge of said slot at a position halfway between the ends of said slot and extending longitudinally along said slot inside of said member and out one end thereof.

9. A broadcast antenna including a hollow conductive cylinder having a length substantially equal to one wavelength at the operating frequency and having a circumference of the order of one-half wavelength, there being a narrow longitudinal lslotialong the length of-saidrcylinflensaid-cylinder having connection-means .thereon to :connect a coaxial transmission line having an linner conductor and .an outer sheath extending: longitudinally from a" position halfway between the-ends 'of fsaid slot and along said slot inside -of-zsaid-cylinder and :out one end o-fsaid cylinder-across said slot, said connection means including rmeans to :connect the outer sheath of said coaxial 'line'alongnone edge of. said slot from one end 'of said antenna to-substantia11 the-midpointrof-saidslot'and theinner conductor of said coaxial: line to the rother edge 'of' said slot across irlomathe end of said outer sheath at substantially thesmidpoint'ofisaidslot.

-10. A broadcast antenna including 7 a :hollow conductive cylinder having "a circumference substantially equal to=a 'half wavelength of. the ioperzating frequency and a length equal to two wave lengths, a: pair of narrow longitudinaltslots exr tending along thelength of said cylinder in an end-to-end relationship,-each of said-slotshaving alength substantially equal to one wavelength, said slots-being closed at each=end,said cylinder having connection means thereon to'-c0nnect coaxial transmission lines each havingan outer sheath-randeaninner conductoracmss the mid- &points :of eachof ssaidslots at the edgesrthereof with thez inner conductoro f one of said lines-crossing said slots in an :opposite direction from; the other.

-WOODROW DARLING.

\ REFERENCES CITED :"Thelfollowing references are of :record 'inL'the file of this patent:

UNITED STATES PATENTS: 

